1. Field of the Invention
The present invention relates to an information recorded disk reproducing apparatus suitable for reproducing optical disks, in particular, optical disks having the same format and different diameters.
2. Description of the Prior Art
As optical disks having the same format and different diameters, the following three types have already been on the market as common ones:
(i) laser disks (LDs) with diameters of 20 cm and 30 cm;
(ii) compact disks (CDs) with diameters of 8 cm and 12 cm; and
(iii) magneto optical disks with diameters of 3.5 inches and 5.25 inches.
Of these disks, the magneto optical disks are put in cases called cartridges having different diameters, so that it is mechanically impossible to reproduce magneto optical disks of different diameters with the same apparatus. However, with respect to the LDs and CDs, the mediums themselves are designed to be directly touched by the user and their reproducing apparatuses do not have any mechanical limitations in reproducing disks of different diameters.
Therefore, unless the diameter is discriminated by some kind of electric means, there caused problems in operating the reproducing apparatus. For example, since disks having different diameters as mentioned above have different moments of inertia, unless the control gain of a motor for rotating the optical disk is changed according to the diameter, an appropriate gain is not obtained for the margin of gain of the motor controlling system. In the worst case, a defect such as hunting is caused.
To avoid such a problem, conventionally, a processing such as changing the gain of the motor controlling system is performed by discriminating the diameter of the optical disk by the following methods:
A first method is such that a reflection type optical sensor such as a photocoupler is arranged at a position outside of the radius of a smaller optical disk when the optical disk is attached to the motor to discriminate the diameter based on the presence/absence of reflected light. PA1 A second method is such that the diameter is discriminated based on the length of the total recording time recorded on an innermost area of the optical disk called a table of contents (TOC). PA1 A third method is such that the optical disk is driven at a constant torque to discriminate the diameter by counting the activation time required for the number of rotations to reach a predetermined value. PA1 A fourth method is such that the diameter is discriminated by a combination of the second and third methods. PA1 According to the first method, an extra part such as the photocoupler is necessary for discriminating the diameter, which leads to an increase in cost. Moreover, since the size of the apparatus increases because of the attachment of the extra part, the reduction in size cannot be realized. PA1 According to the second method, the discrimination is impossible when work or a program of a short recording time is recorded on a disk of a large diameter. PA1 According to the third method, since the user touches the medium itself as described above when an LD or a CD is reproduced, when the motor controlling system is confused by fingerprints or flaws, the activation requires a long time even when a disk of a small diameter is reproduced, so that a mis-discrimination may occur. When a frequency generator is attached to the motor to directly monitor the number of rotations, the frequency generator is an obstacle to the reduction in size and cost like the first method. PA1 According to the fourth method, the defects of the second and third methods are compounded.
However, these conventional methods have the following defects: